1. Field of the Invention
The present invention relates to a method of treating semiconductor substrates by exposing the substrate to a hygroscopic liquid. The treatment minimizes the formation of voids in the fabricated semiconductor.
2. Description of the Related Art
During the fabrication of semiconductors and integrated circuits, it is often necessary to remove liquids such as water or solvents from the semiconductor or integrated circuit. For example, the semiconductor may be exposed to water through contact with aqueous solutions. At least a portion of the water is likely to remain on the semiconductor after the contacting. Alternatively, water may be formed as a reaction product during the chip fabrication. For example, U.S. Pat. Nos. 5,858,880 and 5,874,367 describe a method of planarizing wafers by forming silicon oxide films on the surface of the wafer by reacting silane with hydrogen peroxide to form silicon hydroxide. The silicon hydroxide polymerizes to form a gel containing water and polymers having the general formula Six(OH)y or SixHy(OH)z. More water is formed when the polymers are annealed to form the final SiO2 planarizing layer. The water is normally removed from the planarized wafer by heating.
Removing water from the wafer by heating can lead to structural problems in the wafer. For example, when the planarizing silicon hydroxide polymer gel layer described above is heated and annealed, the layer can crack if the rate of moisture removal is not controlled carefully during the phase transition from a gel to a solid. Controlling the rate of water loss can be achieved by careful temperature control, but this is expensive and time consuming. Alternatively, a silica capping layer can be formed on top of the wafer to control the rate of moisture release. Processing conditions must be controlled carefully to prevent cracking of the polymer layer. There is a need for more convenient and reliable methods of removing water during the processing of wafers.
The semiconductor or integrated circuit may also be exposed to solvents during processing. For example, spin-on layers are formed by spin applying silicon oxide, with or without dopants, in a solvent. The solvent is removed by baking, leaving a planarized SiO2 layer. The layer is subject to cracking during the drying process while the layer undergoes a phase change into a solid layer. There is a need for improved methods of removing solvents from semiconductor substrates without damaging the wafer.